Color filter substrate with color filter pattern and protective layers containing photosensitive polyamide resins

ABSTRACT

An electrode plate structure for a liquid crystal color display is produced by forming a color filter layer of a photosensitive polyamide resin containing a colorant dispersed therein; disposing a protective layer of a photosensitive polyamide resin on the color filter layer; forming an ITO (indium-tin-oxide) film on the protective layer, preferably at an elevated temperature of at most 270° C.; post-annealing the ITO film at a temperature of 200°-300° C. for improving the crystallinity of the ITO film suitable for etching; and selectively etching the ITO film patternwise with an etchant of hydroiodic acid or a hydroiodic acid-ferric chloride aqueous solution mixture to leave an ITO electrode pattern.

This application is a division of application Ser. No. 08/148,335, filedNov. 3, 1992, now U.S. Pat. No. 5,278,683, which is a division ofapplication Ser. No. 07/728,707, filed Jul. 11, 1991, now U.S. Pat. No.5,185,059, issued Feb. 9, 1993.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a process for producing a substrate orelectrode plate structure for a liquid crystal color display device,particularly a process for producing an electrode plate structure for aliquid crystal display device having an electrode pattern of ITO(indium-tin-oxide) formed on a color filter.

As a conventional type of color filter, there has been known a dyedcolor filter which is obtained by coating a substrate with a dyeablelayer of a hydrophilic polymer, such as gelatin, casein, glue orpolyvinyl alcohol, and dyeing the layer with a colorant to form acolored layer.

Such a color filter obtained through a dyeing process encounters adifficulty when it is subjected to a heat treatment as by formation of atransport conductor film of ITO, etc., thereon, because the colorantused in the dyeing has a relatively low heat resistance on the order of150° C.

In the case of forming a layer of ITO, etc., on a color filter, it hasbeen a usual practice to form such a layer at a low temperature inconsideration of the insufficient heat resistance of the color filter.If the formation of an ITO film is effected at a low temperature,however, the crystalline structure of the ITO is not specified, thusrequiring a long time for etching thereof when an ordinary etchingliquid for ITO, such as a hydrochloric acid-ferric chloride mixture, ora hydrochloric acid-nitric acid mixture. As a result, it is extremelydifficult to control the shape of an ITO electrode pattern and also thecolor filter layer formed below the ITO can be damaged due to such along time of etching. These difficulties have provided a seriousobstacle to practical utilization a dyed color filter for a liquidcrystal device.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the problems accompanyingthe conventional process, i.e., poor heat resistance of a color filter,low-temperature formation of an ITO film required thereby andcorresponding difficulty in etching thereof.

Another object of the present invention is to provide a substrate orelectrode plate structure for a liquid crystal color display devicewherein a heat-resistant color filter is patterned in a simple step andan ITO film formed at a low temperature is then post-treated to have agood etching characteristic.

A further object of the present invention is to provide an electrodeplate structure for a liquid crystal color display device wherein an ITOelectrode pattern is formed on a color filter through etching withoutdamaging the color filter.

According to the present invention, there is provided a process forproducing an electrode plate structure for a liquid crystal colordisplay, comprising the steps of:

forming on a substrate a color filter layer comprising a photosensitivepolyamide resin containing a colorant dispersed therein,

coating the color filter layer with a protective layer comprising aphotosensitive polyamide resin,

coating the protective layer with an ITO (indium-tin-oxide) film,

heat-treating the ITO film, and

selectively etching the ITO film patternwise with an etchant comprisinghydroiodic acid or a hydroiodic acid-ferric chloride aqueous solutionmixture to leave an ITO electrode pattern.

According to the present invention, it is possible to form awell-controlled ITO electrode pattern which has been difficult toprovide. Further, it is possible to prevent a color filter pattern of acolored photosensitive polyamide resin formed below an ITO film frombeing damaged during etching, thus providing a reliable electrode platestructure for a liquid crystal color display device at a high yield.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1M are schematic sectional views for illustratingindividual steps involved in a preferred embodiment of the process forproducing an electrode plate structure for a liquid crystal colordisplay device according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the process for producing an electrode plate structure according tothe present invention, first of all, a substrate of, e.g., glass orplastic, is coated with a photosensitive polyamide resin containing acolorant of a prescribed color, preferably an organic pigment.

The photosensitive polyamide resin used herein is a polyamide resinhaving an unsaturated photosensitive group. Preferred examples of thephotosensitive polyamide resin may include polyamides having any one ofthe following aromatic units including an unsaturated photosensitivegroup in addition to amide linkages:

(1) Benzoate units as represented by ##STR1## wherein R₁ :CHX═CY--COO--Z--

X: --H, --C₆ H₅

Y: --H, --CH₃

Z: --C₂ H₅

(2) Benzoate acrylate units as represented by ##STR2## wherein Y: --H,--CH₃

(3) Diphenyl ether units as represented by ##STR3## wherein R₂ :CHX═CY--CONH--, CH₂ ═CY--COO--(CH₂)₂ --OCO--, CH₂ ═CY--COO--CH₂ --

X: --H, --C₆ H₅

Y: --H, --CH₃

Referring to FIGS. 1A to 1M for illustrating an embodiment, a solutionof such a photosensitive polyamide resin in a solvent such asN-methylpyrrolidone containing further a prescribed colorant and aphotopolymerization initiator as desired is applied onto a substrate 1,e.g., by spinner coating and dried to form a colored photosensitivepolyamide layer 2 (FIG. 1A), which is then subjected to ordinaryphotolithographic steps including exposure with ultraviolet rays througha photomask 3 to form a photocured part 2a (FIGS. 1B and 1C) anddeveloping with a solvent for removing the unexposed part to leave acolor pattern 4 (FIG. 1D).

The above steps are repeated for a required number of colors, typicallyR (4), G (5) and B (6) to form a color filter layer in a thickness of,e.g., 1-3 microns (FIG. 1E).

Then, the thus formed color filter layer is further coated with aprotective layer 7 in a thickness of, e.g., 1-3 microns (FIG. 1F). Theprotective layer may also suitably formed by application of aphotosensitive polyamide similar to the one used for constituting thecolor filter but substantially free from a colorant, followed byexposure with ultraviolet rays and preferably post-curing under heatingaround 200° C.

Then, an ITO (indium-tin-oxide) film 8 is formed on the protective layer7 (FIG. 1G). The ITO film may preferably be formed in a thickness of400-2000 Å by vapor deposition, such as sputtering. The sputtering maybe performed at an elevated temperature of 270° C. or lower, preferably250° C. or lower and preferably at least 100° C. The sputtering at suchan elevated temperature on the color filter layer is possible becausethe color filters 4-6 are formed by a colored photosensitive polyamidehaving an excellent heat resistance.

The ITO film thus formed by sputtering at a relatively low temperatureof at most 270° C. is present in an almost amorphous state and cannothave a sufficient crystallinity suitable for etching. Accordingly, ifthe ITO film is subjected to etching with an ordinary etchant, the timerequired for etching is fluctuated and the product quality can beremarkably lowered while requiring a quite long etching time if acomplete degree of etching is desired.

In the present invention, however, the ITO film after the deposition issubjected to post annealing. Preferable conditions for the annealing mayfor example include: gradual heating at a rate of, e.g., 100°-200°C./hour; holding at a temperature of 200°-300° C., preferably around250° C.; and gradual cooling at a rate of, e.g., at most 100° C./hour,preferably at most 50° C./hour. By this annealing treatment, thecrystallinity of the ITO film is improved to provide a good etchingcharacteristic.

Then, the ITO film thus treated is subjected to patterning by ordinarylithographic steps, including formation of a photoresist 9 (FIG. 1H),pattern exposure through a photomask 10 (FIG. 1H), development of theexposed resist (FIG. 1J), etching (FIGS. 1K and 1L) and peeling of theresist to form an electrode plate structure for a liquid crystal colordisplay device including an ITO electrode pattern corresponding to therespective color filter patterns (FIG. 1M).

In the etching step (FIG. 1K) according to the present invention,however, the ITO film is etched by using an etchant comprisinghydroiodic acid or a mixture thereof with ferric chloride aqueoussolution. Compared with an ordinary etchant for ITO, i.e., hydrochloricacid-ferric chloride mixture or hydrochloric acid-nitric acid mixture,the hydroiodic acid or hydroiodic acid-ferric chloride mixture caneasily control the ITO electrode pattern and prevent any deteriorationof the color filter layer comprising the colored photosensitivepolyamide resin below the ITO film, thus allowing the production of anITO electrode pattern having a good shape accuracy at a high yield.

In the hydroiodic acid etchant, the hydrogen iodide may preferably becontained at a concentration of 55-58 wt. %. Further, the hydroiodicacid-ferric chloride aqueous solution mixture etchant may preferably beformed by mixing a hydroiodic acid solution (55-58 wt. %) and a ferricchloride aqueous solution at a ratio of 2:1 to 3:1.

On the thus-prepared electrode plate structure according to the presentinvention as shown in FIG. 1M, a metal electrode may be disposed along aside of each ITO electrode pattern for providing an improvedconductivity, and the entire surface may be further coated with anoptional organic or inorganic insulating film and an organic orinorganic alignment control film, which may be imparted with a uniaxialorientation axis as by rubbing or oblique vapor deposition.

The thus-treated electrode plate structure may be fixed to a similarelectrode plate structure but with no color filter layer with anappropriate spacer therebetween and the periphery thereof is sealed withan epoxy adhesive, etc. to form a cell structure, into which a liquidcrystal is injected through an injection port. Then, the injection portis sealed to form a liquid crystal cell (color display device). Theelectrode plate structure according to the present invention may be usedfor any type of liquid crystals inclusive of a conventional TN-liquidcrystal, basically, but most suitably be used for a ferroelectric liquidcrystal.

Hereinbelow, the present invention will be more specifically describedbased on Examples.

EXAMPLE 1

An electrode plate structure was prepared through the steps as describedwith reference to FIGS. 1A-1M.

Referring to the figures, a glass substrate 1 was provided with colorfilter patterns of R(4), G(5) and B(6) each in a thickness of about 1.5micron (FIG. 1E) through repetition of ordinary lithographic stepsincluding application of a colored photosensitive polyamide resin("PA-1012R", "PA-1012G" and "PA-1012B", available from Ube Kosan K.K.)dissolved in N-methyl-2-pyrrolidone at a viscosity of 90 to 130 cP byspinner coating (FIG. 1A), pattern exposure to ultraviolet rays from anultra high-voltage mercury lamp to form a photocured part 2a (FIG. 1Band 1C), and development with a cyclohexane-based developer solution(FIG. 1D). Then, the color filter layer including the color filterpatterns 4-6 was further coated with a solution of a photosensitivepolyamide resin ("PA-1000C", available from Ube Kosan K.K.), followed bydrying, ultraviolet exposure and post-curing at 200° C. to form an about2 micron-thick protective layer 7.

Then, the above-treated substrate having a color filter pattern thereonwas subjected to sputtering of ITO at a substrate temperature of 250° C.at a deposition pressure of 3×10⁻³ Torr under Ar stream of 200 sccm andO₂ stream of 2 sccm to form an about 1000 Å-thick ITO film 8. Then, thesubstrate having the ITO film 8 was placed in a clean oven, heated to250° C. in 2 hours, held at that temperature for 1 hour and cooledgradually in 4 hours (FIG. 1G).

Then, the ITO film on the substrate was coated with a 1 micron-thickphotoresist film 9 (FIG. 1H), which has then exposed through aprescribed electrode pattern mask (FIG. 1I) and developed with aprescribed developer (FIG. 1J). Then, the substrate having thethus-developed photoresist pattern 9 was dipped in a hydroiodic acidsolution with a concentration of about 56 wt. % at 40° C. for 2 minutesunder a light-shielding condition (FIG. 1K), and then the photoresistpattern 9 was peeled off to form an ITO electrode pattern (FIG. 1L and1M).

The thus formed ITO electrode pattern 9 (FIG. 1M) was free from thinningor irregularity of the pattern due to the etching to retain an accurateshape, and occurrence of short circuit between adjacent electrodes wereextremely rare.

Further, as a result of the use of hydroiodic acid as the etchant, thecolor filter pattern comprising the cured photosensitive polyamide wasnot damaged at all.

EXAMPLE 2

An electrode plate structure was prepared in the same manner as inExample 1 except that the etching of the ITO film was performed for 2.5minutes by using a 70/30-volume mixture of about 56 wt. %-hydroiodicacid solution/35 wt. %-ferric chloride at 40° C. as the etchant.

The thus prepared electrode plate structure has an ITO electrode patternwhich was free from thinning or irregularity of the pattern due to theetching to retain an accurate shape, and occurrence of short-circuitbetween adjacent electrodes were extremely rare.

Further, as a result of the use of a hydroiodic acid-ferric chlorideaqueous solution mixture as the etchant, the color filter patterncomprising the cured photosensitive polyamide was not damaged at all.

Comparative Example

An electrode plate structure was prepared in the same manner as inExample 1 except that the etching of the ITO film was performed for 4minutes by using a mixture of 60 vol. % of hydrochloric acid and 40 vol.% of ferric chloride aqueous solution (Fe₂ Cl₃ 35 wt. %) at 47° C.

The thus-prepared electrode plate structure had an ITO electrode patternwhich was accompanied with remarkable thinning of the pattern due toside etching, thus failing to provide a prescribed electrode width.

Further, as a result of the use of the hydrochloric acid-ferric chlorideaqueous solution mixture, the color filter pattern comprising the curedphotosensitive polyamide was accompanied with partial peeling or liftingalong with a damage of the protective film, so that the resultantelectrode plate structure was practically unacceptable at all.

What is claimed is:
 1. A color filter substrate, comprising:(i) a colorfilter pattern formed from a photosensitive polyamide resin containing acolorant dispersed therein, (ii) a protective layer formed from aphotosensitive polyamide resin, and (iii) an indium-tin oxide film.
 2. Acolor filter substrate according to claim 1, wherein said indium-tinoxide film has been patterned after heating and annealing treatment. 3.A color filter substrate according to one of claims 1 or 2, wherein saidprotective layer comprises a cured film of a photosensitive polyamideincluding a photosensitive unit selected from the group consistingof:(1) benzoate units represented by ##STR4## wherein R₁ isCHX═CY--COO--Z-- (wherein X is H or C₆ H₅, Y is H or CH₃ and Z is C₂H₅); (2) benzoate acrylate units represented by ##STR5## (3) diphenylether units represented by ##STR6## wherein R₂ is independentlyCHX═CY--CONH--, CH₂ ═CY--COO--(CH₂)₂ --OCO--, or CH₂ ═CY--COO--CH₂ --.4. A color filter substrate according to one of claims 1 or 2, whereinsaid ITO film has been patterned with a etching solution containinghydroiodic acid at a concentration of 55-58 wt. %.
 5. A color filtersubstrate according to one of claims 1 or 2, wherein said ITO film hasbeen patterned with an etching solution comprising an admixture of from2-3 parts of solution containing hydroiodic acid at a concentration of55-58 wt. % with 1 part of an aqueous solution containing ferricchloride.
 6. A color filter substrate according to claim 2, wherein saidheating and annealing treatment comprises:(i) heating said indium-tinoxide film to a temperature of 200°-300° C., and (ii) cooling saidindium-tin oxide film at a rate of at most 100° C./hour.